To record data to an optical disc which is a disc-shaped recording medium, a guiding means is required for forming a recording track. To this end, pregrooves are preformed on the optical disc and the groove itself or a land, of which the cross section is trapezoidal, between the preformed grooves is used as the recording track.
Address information has to be recorded on an optical disc of this type to permit recording of data in a given position on a recording track on the optical disc. In some cases, such address information is recorded on the optical disc by wobbling a groove. Namely, a data recording track is preformed as a pregroove for example on the optical disc while the lateral wall of the pregroove is being wobbled correspondingly to the address information. Thus, for recording or reproducing data to or from the optical disc, an address to which the data is to be written or from which the data is to be read can be read from wobbling information provided as return light information, and the data can be written to a desired position or read from a desired position without having to preform pit data or the like indicating an address, for example, on the recording track.
By additionally recording address information as a wobbled groove, it will be unnecessary to discretely define an address area on a track and record an address as pit data in such address area, for example. Therefore, the actual capacity of the optical disc for recording data can be increased for the address area which is thus made unnecessary.
Absolute time (address) information represented by such a wobbled groove is called ATIP (absolute time in pregroove) or ADIP (address in pregroove).
Optical discs having such a wobbled groove formed thereon include CD-R (CD-Recordable), CD-RW (CD-Rewritable), DVD-R, CD-RW, DVD+RW, etc. In these types of optical discs, however, address information is additionally recorded as a wobbled groove in a manner different from one type to another of these optical discs.
In CD-R and CD-RW, the groove is wobbled according to a signal generated by making FM modulation of address information.
ATIP information embedded in a wobbled groove formed on CD-R/CD-RW is subjected to biphase modulation before the FM modulation as shown in FIG. 1. More specifically, the biphase modulation is such that ATIP data such as an address or the like is changed in state between “1” and “0” in each predetermined cycle by the biphase modulation and its ratio between average numbers of “1” and“0” is 1:1, and a wobbling signal of 22.05 kHz in average frequency are generated by the FM modulation of the ATIP data.
A groove defining a recording track is wobbled according to such an FM modulation signal.
In DVD-RW which is a phase-change recording-based rewritable version of DVD (digital versatile disc) and DVD-R which is an organic dye change-based recordable version of DVD, wobbled grooves G are formed as preformatted on the disc and a land prepit LPP is formed in a land between the grooves G, as shown in FIG. 2.
In this case, the wobbled groove is used to control the rotation of the disc and generate a recording master clock or for similar purposes, and the land prepit is used to determine an accurate recording position in bits and acquire a variety of information about the disc such as a pre-address etc. In this case, the pieces of address information themselves are recorded as land prepits LPP, not as wobbles of the groove.
In DVD-RAM which is the phase change recordable version of DVD, information such as an address is recorded as a groove wobbled based on the phase modulation (PSK modulation) on the disc.
FIGS. 3A to 3C show information represented by phase modulation-based wobbles of the groove. As shown in FIGS. 3A to 3C, eight wobbles are taken as one ADIP unit. Each of the wobbles is phase-modulated for a positive wobble PW and negative wobble NW to take place alternately in a predetermined order, so that the ADIP unit represents a sync pattern or data “0” or “1”.
Note that the positive wobble PW is a wobble whose leading end is directed toward the inner circumference of the disc, and the negative wobble NW is a wobble whose leading end is directed toward the outer-circumference of the disc.
FIG. 3A shows a sync pattern (ADIP sync unit). In this sync pattern, the former four wobbles (W0 to W3) are negative ones NW and the latter four wobbles (W4 to W7) are positive ones PW.
FIG. 3B shows an ADIP data unit being the data “0”. In this ADIP data unit, the leading wobble W0 is a negative one NW as a bit sync, it is followed by three wobbles W1 to W3 as positive ones PW, and the latter four wobbles include two wobbles W4 and W5 as positive wobbles PW and two wobbles W6 and W7 as negative ones NW. Thus, the ADIP data unit represents data “0”.
FIG. 3C shows an ADIP data unit being the data “1”. In this ADIP data unit, the leading wobble W0 is a negative one NW as a bit sync, it is followed by three wobbles W1 to W3 as positive ones PW, and the latter four wobbles include two wobbles W6 and W7 as negative ones NW and two wobbles W6 and W7 as positive ones PW. Thus, the ADIP data unit represents data “1”.
These ADIP units represent together one channel bit, and a predetermined number of such ADIP units represents an address or the like.
However, the above wobbling techniques are not advantageous as follows:
First, in case a groove is wobbled according to FM modulation data as in CD-R and CD-RW, the stroke of a wobble of an adjacent track will cause a phase change of the FM waveform. Thus, in case the track pitch is reduced, an address as ATIP data cannot be reproduced well. In other words, the FM modulation data-based wobbling cannot suitably be used in case the track pitch is narrowed for an improved recording density.
Next, in case land prepits are formed as in DVD-R and DVD-RW, the land prepits may possibly have a cross talk into a read RF signal, causing a data error and mastering (cutting) has to be done for the groove and land prepits (2-beam mastering). This is relatively difficult to implement.
Further, in case a groove is wobbled according to PSK data as in DVD-RW, the RF component at the phase-change point of a PSK modulation wave may possibly have a crosstalk into a read RF signal, causing a critical error.
Also, since the PSK phase shift point has an extremely high frequency component, the essential frequency band of a wobbling signal processing circuit system will be higher.